The CSIRO/AMIRA P223 codes solve your problem.

http://p223suite.sourceforge.net/

Dear Kimmo, thank you for your suggestion. I tried to download some software (it is not clear in the site the applicability of the available software), but I received the message "The page cannot be found".

Paulo, they should be available but it seems that the download links are broken. I suggest that you contact them. In your case, Beowulf could be the right choice.

Have you tried EM1DTM from UBC?

http://www.eos.ubc.ca/ubcgif/iag/sftwrdocs/em1dtm/em1dtm-descrip.htm

University of Aarhus has a program called EMMA

http://hgg.au.dk/download/emma/

Interpex limited 1Dinterpretation

Dear Kimmo, I got Beowulf.

Dear Richard and Stefan, thank you for your information.

Dear Hebbache, I was not able to make Interpex work with my computer.

Dear Paolo, would you please tell me whether Beowulf is doing well or not.  I actually need free software for 1D TDEM modeling but all I tried was not good.

I am trying to download it but it gives page not found error. Would you please tell me how did you obtained it.

Hi Paulo,

EMMA  from Aarhus is fine. Also I recently heard that Zond (from Russia) provides free access to software (with some restriction) but I never tried it: http://zond-geo.ru/english/zond-software/electromagnetic-sounding/zondtem1d/

Thank you Carole, I downloaded the software. Let's see if it works.

Yeah Zond TEM is a good option with some restrictions. EMMA is probably the most used free. I use IX1D with license, works for me.

SimPEGEM1D is a free open-source package in Python for simulation and inversion of Frequency and Time Domain EM data, https://github.com/simpeg/simpegEM1D

You can also check out empymod: https://empymod.github.io/

Dear Thubaut and Julian, thanks for your suggestion. I downloaded both softwares and I will try them.